RV Battery Bank Calculator

The calculator converts each appliance's daily energy use to amp-hours at your system voltage, sums the total, then divides by the usable depth of discharge for your chosen chemistry.

LFP uses 85% DoD and AGM uses 50% DoD by default. The result is scaled by your autonomy days and includes a 20% efficiency margin for wiring and inverter losses.

How many amp hours do I need for boondocking?

Start by listing every appliance in your RV and its daily run hours. Multiply watts × hours for each to get watt-hours, then divide by your system voltage (typically 12V) to convert to amp-hours. Add 20% for efficiency losses, then divide by your usable depth of discharge — 80–90% for LFP lithium, 50% for AGM. A typical weekend boondocker with a refrigerator, lights, and phone charging usually needs 100–200Ah of LFP or 200–400Ah of AGM for a two-night stay.

What is the difference between LFP and AGM batteries for RVs?

LFP (lithium iron phosphate) batteries offer roughly twice the usable capacity at half the weight compared to AGM at the same amp-hour rating. A 100Ah LFP battery can safely discharge to 90–100Ah of usable energy; a 100Ah AGM is limited to about 50Ah before damage occurs. LFP also has a longer cycle life (2,000–5,000 cycles vs 400–800 for AGM) and charges faster. AGM costs less upfront and does not require a battery management system, making it simpler for budget builds or occasional use.

How long will my RV battery last overnight?

Divide your usable battery capacity (Ah × DoD) by your average overnight draw in amps. For example, a 200Ah LFP battery (180Ah usable) powering a 5A refrigerator compressor and 2A of miscellaneous loads gives roughly 25 hours — more than enough for one night. A 12V roof air conditioner draws 15–20A and would drain the same battery in 9–12 hours, making it impractical without shore power or a generator.

Can I replace my RV's AGM battery with lithium?

Yes, but you may need to update your charger and converter. Many older RV converters use a charge profile designed for lead-acid chemistry that can overcharge LFP cells or fail to reach full charge. Look for a converter with a lithium or LFP charge profile, or add a dedicated DC-DC charger between your alternator and lithium bank. Also verify that your solar charge controller supports LFP — most MPPT controllers made in the last five years do.

What does depth of discharge mean for RV batteries?

Depth of discharge (DoD) is the percentage of a battery's rated capacity you can safely use before recharging. AGM batteries should not be discharged below 50% DoD without shortening their cycle life significantly. LFP batteries can safely reach 80–90% DoD. In practice, this means a 200Ah AGM bank gives you only 100Ah of usable energy, while a 200Ah LFP bank gives 160–180Ah. The calculator applies the correct DoD for each chemistry automatically.